Field
Embodiments of the present invention generally relate to supporting substrates in processing chambers.
Description of the Related Art
During processing, substrates are positioned on a susceptor within a process chamber. The susceptor is supported by a susceptor support shaft, which is rotatable about a central axis. The susceptor support shaft includes multiple arms extending therefrom—usually three to six—which support the susceptor. As the susceptor support shaft is rotated during processing, the arms extending from the susceptor support shaft interrupt a pyrometer beam used to measure a temperature of the susceptor or the substrate, thus causing the interference of pyrometer readings. Even though the arms may be formed from quartz, which is generally optically transparent, at least some amount of light is absorbed by the arms, and thus, is not completely optically transparent. This amount of light absorbed and scattered by the arms affects the amount of light transmitted by the pyrometer beam to the susceptor, and thus, affects the accuracy of the temperature measurement by the pyrometer. As the susceptor support shaft rotates, there are periods when the arm is within the pyrometer beam path, and periods when the arm is adjacent to the pyrometer beam path. Thus, the amount of light from the pyrometer beam reaching the susceptor varies as the susceptor support rotates, resulting in periods of inaccurate temperature measurement.
An IR pyrometry system is normally used for the sensing of radiation emitted from the backside of susceptor or a substrate, the pyrometer reading is then converted to temperature based on the surface emissivity of the susceptor or substrate. A software filter is normally used to reduce interference with temperature ripples (due to the support arms move in and out the pyrometer beam during the rotation mentioned above) to around ±1 degree Celsius. The software filter is also used with an algorithm including average data in sample window a couple of seconds wide.
With the advanced cyclic EPI process, the process temperature will change as per recipe step and recipe step time is getting shorter. Therefore, the time delay of the software filter needs to be minimized and a much narrower sample window is required to improve dynamic response of temperature variations. The temperature ripple needs to be further reduced to less than ±0.5 degree Celsius range for optimum cycle to cycle temperature repeatability.
Therefore, there is a need for an apparatus which enables more accurate temperature measurement.